Composite propellant including (u) polyfunctional amine

ABSTRACT

Propellant compositions are provided in which dewetting of the propellant composition under applied stress is substantially reduced. Reduced dewetting is achieved through the use of polyfunctional amines which are capable of forming a chemical bond between the oxidizer (oxygen containing ammonium salt) and the binder in the cured propellant.

Elite tats Ptemt 1191 Dehm Feb. 5, 1974 [54] COMPOSITE PROPELLANT KNCLUDHNG 3,454,436 7 1967 Bedell 149/19 (U) POLYFUNCTHONAL A E 3,529,042 9/1970 Lippert 3,476,622 11/1969 Harada et a1. lnvemori Henry Dehm, Salt Lake y, 3,586,552 6/1971 Potts a a1 149/19 Utah [73] Assignee: Hercules Incorporated, Wilmington, Primary Examiner-Carl D. Quarforth Del. Assistant ExaminerE. A. Miller [22] Filed y 22 1970 Attorney, Agent, or Firm-Michael B. Keehan 21 A l.N .187513 1 pp 57 ABSTRACT [52 U.S. c1 149/19 149/36 149/60 ProP?ant P are Pmvided in which dewei- 149/76 ting of the propellant composition under applied stress 51 1m. (:1 C06d 5/06 is substantially reduced- Reduced deweiiiiig is 58 Field of Search 149/19 76 36 60 achieved through the use of Poiyfunciionai amines i which are capable of forming a chemical bond be- [56] References Cited tween the oxidizer (oxygen containing ammonium UNITED STATES PATENTS salt) and the binder in the cured propellant.

3,305,523 2/1967 Burnside 149/19 X i 11 Claims, N0 Drawings COMPOSITE PROPELLANT INCLUDENG (U) POLYFUNCTIONAL AMINE This invention relates to novel composite propellant compositions having superior load bearing properties, stability, and mechanical properties. The propellant of this invention comprises in the form of a cured admixture a crosslinkable binder prepolymer, a crosslinking agent, an oxygen containing ammonium salt and a polyfunctional amine which contains at least one amine group more basic than ammonia and at least one amine group which is reactive with the polymeric binder. More particularly, this invention relates to composite propellant compositions in which dewetting of the propellant composition is substantially reduced through the incorporation of certain polyfunctional amines in controlled amounts, said polyfunctional amines capable of providing a primary chemical bond between the surface of the oxygen containing ammonium salt and propellant binder in the cured propellant.

Composite solid propellants are comprised of oxidizers and fuels in the form of small solid particles, sometimes referred to hereinafter as fillers, uniformly distributed in a polymeric binder. The polymeric binder functions to hold and uniformly distribute the tiller particles throughout the binder.

Mechanical and ballistic properties of propellants are of primary importance in the selection of a propellant for any particular use. Mechanical and ballistic properties are known to depend on the nature of the interface between the solid filler particles and the polymeric binder. It has been discovered by various researchers in the field of solid propellants that mechanical failure of solid propellants resulting from environmental and operating stresses usually occurs at or about the binderfiller interface within the cured propellant matrix rather than in the propellant binder. Failure of composite propellant at the binder-filler interface is referred to as dewetting.

Studies by Oberth and Bruenne'r reported in CPIA Publication No. 94C, Vol. 11, dated October 1965, show that subscale motors containing propellants that fail in the binder phase of the propellant have markedly improved recycle properties compared to substantially identical propellants that dewet at the binder-filler interface under similar stress conditions. Still other studies have shown that composite propellants that fail under conditions of high stress exclusively in the binder I phase rather than at the binder-filler interface exhibit markedly improved load bearing capability and, in general, are physically more stable propellants. Failure of propellants in the binder phase rather than at the binder-filler interface was achieved employing various additives which function to bond the ammonium perchlorate oxidizer to the propellant binder.

In some of the studies conducted by Oberth and Bruenner, triethanolamine was employed in an attempt to eliminate dewetting. While improved mechanical properties were achieved in a polyurethane binder employing triethanolamine as an additive, evolution of ammonia gas from these propellants caused difficulties in curing and in reproducibility of mechanical properties and resulted in porous propellant. Another additive employed in an attempt to reduce binder-filler dewetting was dihyoroxypropyl-bis-Z-cyanoethylamine. This material was considered superior to triethanolamine for use in polyurethane type composite propellants because ammonia was not liberated as reaction product during mixing and cure of the composition. Recent studies by C. 0. Parker and T. E. Stevens reported in Redstone Research Laboratories Technical Report 8-205 of January 1969 show that use of dihydroxypropyl-bis-2-cyanoethylamine increases the mix viscosity of composite propellant and complicates propellant processing.

Broadly, in accordance with this invention, composite propellant compositions are provided in which the tendency of the propellant to dewet under conditions of stress is substantially reduced, said propellant compositions comprising in the form of a cured admixture a crosslinkable binder prepolymer, a crosslinking agent, an oxygen containing ammonium salt selected from the group consisting of ammonium perchlorate, ammonium nitrate, hydrazine perchlorate and hydrazine diperchlorate, and a polyfunctional amine having at least one amine group more basic than ammonia and at least one amine group reactive with and available for reaction with the polymeric binder after ammonia has been displaced from the surface of the oxygencontaining ammonium salt. The composite propellant compositions of this invention comprise by weight in the form of a cured admixture from about 60 to about percent of oxygen-containing ammonium salt, from about 5 to about 20 percent of a crosslinkable binder prepolymer and crosslinking agent and from about 0.005 to about 0.05 percent of a polyfunctional amine. These compositions can optionally contain a metal or metal hydride fuel in amounts of from 0 to about 20 percent by weight.

The polyfunctional amines which can be employed in this invention include amines having one or more aliphatic amine groups which are more strongly basic than ammonia and at least one primary aromatic amine group which is less basic than ammonia; and polyfunctional aliphatic amines containing primary and secondary amine groups in which all of the amine groups are more basic than ammonia, but for steric or electronic reasons at least one of the secondary aliphatic amine groups remains free, i.e., it will not displace ammonia from the surface of ammonium perchlorate. The free amine group(s) of this latter class of amines are available to react with polymeric binder.

Illustrative polyfunctional amines defined above have the following structural formula:

where X is either LL Jy l wherein Ar is phenylene, amino-substituted phenylene, naphthylene, amino-substituted naphthylene; m is from 1 to 20, n is from 2 to 5, y is from 1 to 5 and R is hydrogen or lower alkyl having from one to four carbon atoms.

A preferred class of polyfunctional amines having the general formula I-a has the structural formula set forth below:

where z is 0,1, 2, 3 or 4.

Illustrative polyfunctional amines which can be employed in the compositions of this invention wherein X of the general formula I is group (I-a) defined above include B -(4-aminophenyl) ethylamine; triaminophenyl) butylamine, ,B-(2,4-diaminophenyl) hexylamine; ,8- (4-aminophenyl) decylamine; B-(Z, 4-diaminophenyl) tetradecylamine; 2-amino-7-naphthalenethylamine; 2-amin0-7-naphthalenebutylamine; 3,5-diamino-6-naphthalenedecylamine and the like. Illustrative polyfunctional amines of formula I wherein X is group (I-b) defined above include diethylenetriamine, triethylenetetramine; tetraethylenepentamine, pentaethylenehexamine, and the like. Another suitable polyfunctional amine is polyethyleneimine. This polyfunctional amine is available commercially @QE e IE L .UT1UlQ.:MQDIQ Binder systems which can be employed in the propellant compositions of this invention include all binder systems which are reactive with the polyfunctional amines described herein. These binders include those derived from polyester prepolymers such as polyesters having terminal carboxy groups and which are linear condensation products of polyhydric alcohols and polybasic acids such as set forth in US. Pat. No. 3,155,552; polyurethane binders prepared by reaction of a compound having two or more hydroxyl or thiol groups with an organic compound having two or more isocyanate or isothiocyanate groups such as disclosed in US. Pat. No. 3,296,043; and polymeric binders derived from carboxy-terminated prepolymers fully described hereinafter. The number of functional groups on at least a portion of the binder prepolymer and/or crosslinking agent must be greater than 2 so that a crosslinked propellant composition results.

Illustrative binder prepolymers and crosslinkings agents which will react with the polyfunctional amines hereinabove defined to produce the propellant compositions of this invention are set forth in Table I which follows.

TABLE I Prepolymer Curing agent functional functional group group rereacting in the acting in the curing reaction curing Binder prepolymer reaction Carboxyl-terminated polybuta- Carboxyl.... Epxide,imine.

y- Do.

acrylate ester. 7, .4

TABLE I -Cominucd Prepolymer Curingngentfunctional functionnlgronp group rereacting in the acting in the curing reaction curing Binder prepolymer reaction 12. Ethyl acrylatel1ydroxyethyl .....d0 Do.

acrylate copolymer (hydrocarbon backbone). 13. Hydroxyl-terminated fiuoro- .do Do.

carbon. 14.... Hydroxyl-terminated polyester ....do Do.

(polyester backbone) as in U.S. 3,296,043, col. 10, lines 62:75; col. 11, lines 1-30. 15. Low molecular weight diols .do..." D0.

(U.S. 3,296,043, col. 10, lines 7-61 16.... I-Iydroxyl-terminatcd polyether ..do Do. 17. Hydroxyl-tcrminatcd polysul- ..do Do.

fide (as in U.S. 3,296,043, col. 11, lines 33-37). Nitrocellulose ..do Do. Isocyanate-terrninatcd poly- Isocyanato.. Hydroxyl.

ester (polyester backbone).

1 As in U.S. 3,296,043, col. 12, lines 11-24. W

Binder prepolymers 1-7 in Table I cure principally via the epoxide-carboxyl reaction. Binder prepolymers 8-18 cure via formation of urethane linkages from the interaction of hydroxyl and isocyanate groups. Binder prepolymer 19 cures via an isocyanate hydroxyl reaction.

Crosslinking agents which can be employed with the crosslinkable propellant binder prepolymer to effect Crosslinking thereof and which will react with the polyfunctional amine to provide a chemical bond between the polyfunctional amine and the propellant binder when in a cured admixture include polyisocyanates, polyisothiocyanates, polyepoxides, and polyimines.

Illustrative polyisocyanates which can be employed include alkane diisocyanates, such as: ethylene diisocyanate and trimethylene diisocyanate; alkene diisocyanates such as l-propylene-l,2-diisocyanate and 2-propylene-l ,2-diisocyanate; alkylidene diisocyanates such as ethylidene diisocyanate; cycloalkylene diisocyanates; cycloalkylidene diisocyanates; aromatic diisocyanates such as m-phenylene diisocyanate; 2,4- tolylene diisocyanate and 2,6-tolylene diisocyanate; aliphatic-aromatic diisocyanates such as xylene-1,4-

diisocyanate, mixtures thereof and the like. Polyisothiocyanates corresponding to the polyisocyanates described hereinabove can be employed in place of a polyisocyanate crosslinking agent. H

Illustrative polyimines which can be employed as cross-linking agents include the alkyleneimine tris-1,2- methyl aziridinyl phosphine oxide sold under the tradename MAPO; tris-l ,Z-methyl aziridinyl phosphine sulfide; ethylene glycol-bis-B-propylene imine propionate; and terephtaloyl-bis-ethylene imine, mixtures thereof and the like.

Illustrative polyepoxides which can be employed are preferably mixtures of di and triepoxides fully defined hereinafter. Any of the diepoxides and triepoxide mixtures set forth herein can be employed for binder systems other than the preferred binder referred to hereinafter.

The preferred binder prepolymer to be employed in I this invention is a carboxy-terminated prepolymer containing on the average not less than about two free carboxyl groups per polymer molecule and is preferably a homopolyrner of an olefin such as isobutylene or a conjugated diene containing four to eight carbon atoms, such as butadiene-l,3; isoprene; octadiene-1,3 and the like; a copolymer of more than one olefin or conjugated diene such as an ethylene-propylene copolymer; a copolymer of a conjugated diene with other copolymerizable monomers which are preferably vinylsubstituted aromatic compounds such as styrene, the lor 2-vinyl naphthalenes and their alkyl, aryl, alkoxy, cy cloalkyl, alkaryl, aralkyl, aryloxy, and dialkyl amino derivatives; or a mixture of any of the above homopolymers or copolymers.

The preferred carboxy-terminated prepolymers can be produced in known manner from the above monomers, as, for example, by carrying out the polymerization in the presence of, as initiators, organoalkali metal compounds of the formula RM where R is an aliphatic, cycloaliphatic or aromatic hydrocarbon radical, M is an alkali metal such as sodium, potassium, lithium, cesium, or rubidium, and v is 2 to 4, and then replacing the alkali metal atoms on the ends of the polymer molecule with COOH groups by reacting with carbon dioxide and then hydrolyzing. Polymers containing two or more carboxyl groups per polymer molecule can be prepared by polymerizing an unsaturated carboxylic acid containing a single carbon to carbon double bond such as acrylic, methacrylic, itaconic, vinyl acetic, oleic, fumaric, maleic, and like acids with itself or with a different copolymerizable monomer such as, for example, a different unsaturated acid, an olefin or a conjugated diene, according to any of the known methods.

The carboxy-te rminated prepolymers which are par ticularly useful in this invention are the carboxyterminated polymers of butadiene and isobutylene,

having molecular weights ranging from about 1,000 to about 20,000, and preferably from about 3,000 to about 10,000.

The curing agent which is employed in curing the preferred prepolymer of this invention is a mixture of diepoxides and triepoxides having a diepoxideztriepoxide mole ratio of from about 15:1 to 1:1, and preferably from 8:1 to 3:1. Maintenance of the ratio of the difunctional epoxides to the trifunctional epoxides within the above ranges is important to the production of propellants having a satisfactory mechanical property balance since below the ratio of 1:1 the propellant elongation is low, and above the ratio of 15:1 the propellant tensile strength is low.

Illustrative diepoxides which can be employed are the saturated or unsaturated aliphatic, cycloaliphatic, aromatic or heterocyclic diepoxides which also contain, if desired, non-interfering substituents. Preferred diepoxides are the aliphatic diepoxides containing four to 30 carbon atoms, the cycloaliphatic diepoxides containing 12 to 40 carbon atoms and the diglycidyl ethers of dihydric phenols. Typical diepoxides include butadiene dioxide; l,2,5,6-diepoxyhexane; diglycidyl ether; diglycidyl ether of 1,3-butanediol; l,8-bis(2,3- epoxypropoxy) octane; l,4-bis(2,3-epoxypropoxy) cyclohexane; 1,4-bis(3,4-epoxybutoxy)-2- chlorocyclohexane; the di(epoxycyclohexanecarboxylates) of aliphatic diols exemplified by the bis(3,4- epoxycyclohexanecarboxylate) of 1,5-pentanedio1, S-methyl-l ,S-pentanediol, 2-methoxymethyl-2,4- dimethyl-l,S-pentanediol; ethylene glycol, 2,2-diethyl- 1,3-propanediol; 1,6-hexanediol and Z-butene-l ,4-dio1; the oxyalkylene glycol epoxycyclohexanecarboxylates exemplified v by bis(2-ethylhexyl-4,5- epoxycyclohexane-1,2-dicarboxylate) of dipropylene glycol, bis( 3,4-epoxy-6-mcthylcyclohexanecarboxylate) of diethylene glycol and bis(3,4-epoxycyclohexanecarboxylate) of triethylene glycol; the epoxycyclohexylalkyl epoxycyclohexanecarboxylates exemplifled by 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate; 3 ,4-epoxyl -methylcyclohexylmethyl 3,4-epoxy-l-methyl cyclohexanecarboxylate; 3,4- epoxy-2-methylcyclohexylmethyl 3,4-epoxy-2- methylcyclohexanecarboxylate; 3,4-epoxy-6-methylcyclohexylmethyl 3,4-epoxy-6-methylcyclohexanecarboxylate; (lchloro-3,4-epoxycyclohexan-l-yl) methyl l-chloro-3,4-epoxycyclohexanecarboxylate; l-bromo- 3 ,4-epoxycyclohexanl -yl) methyl l-bromo-3 ,4- epoxycyclohexanecarboxylate and l-chloro-Z-methyl- 4,5-epoxycyclohexan-l-yl) methyl l-chloro-Z-methyl- 4,5-epoxycyclohexanecarboxylate; epoxycyclohexylalkyl'dicarboxylates exemplified by bis(3,4-epoxycyclohexylmethyl) pimelate and oxalate and bis(3,4- epoxy-6-methylcyclohexylmethyl) maleate, succinate, sebacate and adipate; epoxycyclohexylalkyl phenylenedicarboxylates exemplified by bis(3,4- epoxycyclohexylmethyl) terephthalate and bis(3,4- epoxy-6-methylcyclohexylmethyl) terephthalate; bis(- 3,4-epoxy-6-methylcyclohexylmethyl) diethylene glycol ether; vinyl cyclohexene dioxide; diepoxide of dicyclohexene; dicyclopentadiene dioxide; bis(2,3-epoxycyclopentyl) ether; glycidyl 2,3-epoxycyclopentyl ether; 2,3-epoxycyclopentyl 2'-methylglycidyl ether; l,2,5,6-diepoxy-3-hexyne; 1,3-epoxypropoxy) benzene; l,4-bis(2,3-epoxypropoxy) benzene; 1,3-bis(4,5-

epoxypentoxy)-5-chlorobenzene; 4,4-bis-( 2,3- epoxypropoxy) diphenylether; 2,2-bis( 2,3-epoxypropoxyphenyl) methane; 2,2-bis[p-(2,3-

epoxypropoxy) phenyl] propane, i.e., the diglycidyl ether of bisphenol A; quinoline diepoxide and the like, as well as mixtures thereof.

Triepoxides can be employed and contain three epoxide groups per molecule and are aliphatic, cycloaliphatic or aromatic triepoxides. Preferred triepoxides are the triepoxyalkanes containing six to 25 carbon atoms; the triepoxycyclohexane carboxylates and the triglycidylethers of trihydric alcohols such as glycerol, 1 ,1,l-tri(hydroxymethyl) propane, 1,2,6-hexanetriol and the higher alcohols containing up to about 25 carbon atoms; and the triglycidyl ethers of trihydric phenols, such as phloroglucinol, the trihydroxydiphenyl methanes and propanes, the trihydroxyaminophenols, the trisphenols; mixtures thereof and the like. Epoxide mixtures containing the diglycidyl ethers of bisphenol A and the triepoxides of the aminophenols are particularly preferred.

For best results, both the diepoxide and the triepoxide of the mixture will be in the relatively pure state, i.e., having a purity of about to percent. The ratio of the epoxy groups in the epoxide mixture to the functional groups of the resin binder should be in substantially stoichiometric proportions. Although a slight excess of either is not harmful, it is preferred that a slight excess of epoxy groups over resin binder functional groups be present in the binder.

When employing carboxy-terminated prepolymer as the binder with an epoxide mixture as the crosslinking agent, the presence of a-catalyst is required which promotes the carboxyl-epoxide reaction. The catalyst must also have high activity in the presence of the other propellant ingredients and must not adversely affect the desirable properties of the cured propellant, as by side reactions. Catalysts which have been found to fit all of the above requirements are chromium salts of aliphatic carboxylic acids containing two to 22 carbon atoms are preferably two to 18 carbon atoms, chromium naphthenate or vanadium naphthenate. The preferred catalysts include chromium acetate, chromium 2- ethylhexanoate, chromium neodecanoate, chromium stearate, chromium oleate, chromium naphthenate and vanadium naphthenate. The amount of catalyst necessary to promote the reaction will, of course, depend on many factors, as for example, on the particular metal salt employed, the binder materials and other propellant ingredients present, and the cure rate desired. In general, the amount of catalyst utilized will vary from a very small catalytic amount up to about 0.1 percent of the propellant composition and preferably will be from about 0.005 to about 0.03 percent by weight of the composition.

The composite propellant of this invention is prepared by intimately blending or mixing the ingredients heretofore described using conventional techniques and standard equipment. The solid propellant compositions of this invention are prepared by admixing the binder forming ingredients comprising a prepolymer and a crosslinking agent therefor and a polyfunctional organic amine as defined herein. To this admixture is added the oxygen containing ammonium salt. As is often the case in preparing composite propellants, the oxygen containing ammonium salt may be added in more than one particle size in order to effectively control the cured propellant burning rate. When employing oxidizer having more than one particle size range it is generally preferable to admix the oxidizer having the smallest average particle size last, since the smallest particles have the highest surface to mass ratio and will scavenge the polyfunctional organic amine from the admixture. The order of mixing of ingredients as set forth can be varied. For example, when the polyfunctional amine additive reacts with the binder forming ingredients at a much faster rate than with the oxygen containing ammonium salt, it is generally preferable to add the polyfunctional amine after the oxidizer has been admixed with the binder forming ingredients.

The following examples will more fully illustrate this invention. All parts and percentages are by weight unless otherwise specified.

Examples 1-6 A binder solution is prepared by admixing 0.0108

parts of a chromium 2-ethylhexanoate catalyst containing 10.95 percent chromium into 7.727 parts of a carboxy-terminated polybutadiene having a molecular weight of about 6,000, and a carboxyl content of 1.48 to 1.53 equivalents per grams of polybutadiene and containing 1.0 to 1.5 percent 2,2-methylene-bis(4- methyl-6-tert-butyl) phenol as antioxidant. An epoxide crosslinking mixture is added in several increments with stirring after each addition. Two plasticizers comprising 1.906 parts dioctyl adipate and 1.906 parts of a random polymer of butadiene are then added to the binder mixture. The epoxide mixture is a solution of diepoxides having an epoxy equivalency of 156 and 89 percent pure, and a triepoxide having an epoxy equivalency of 103 and 99 percent pure. To this binder solution is added a polyfunctional amine as specified in Table I. The resulting admixture is agitated until the polyfunctional amine is completely dispersed and dis solved in the binder. Mixing time required is generally from about 15 20 minutes.

Following preparation of the binder mixture the solid ingredients are added as follows. Aluminum is added to the binder mixture and mixed for about 3 minutes. Ammonium perchlorate is added to the binder in three particle size ranges. Ammonium perchlorate having an average particle size of 200a and 400p is added to the binder and aluminum mixture and the resulting propellant matrix is agitated under a reduced pressure of 2.4 mm Hg for about 15 minutes. Ammonium perchlorate having an average particle size of 10p. is then added to the propellant matrix and mixing is continued for an additional 15 minutes under a reduced pressure of 2.4 mm Hg. The resulting propellant is cast into a JANAF dogbone mold preheated at F. The cast propellant is deareated at reduced pressure of about 2.4 mm Hg for 1 hour. The propellant containing mold is sealed in a polyethylene bag containing a drying agent and the propellant is cured at 180F. for 7 days. The cured propellant is cooled to ambient temperature and is cut into 0.25 inch thick dogbone test samples. These dogbones are stored over a drying agent at the testing temperature. These dogbones are tested for mechanical properties employing an Instron Tester at the temperatures set forth in Table 11. Details of the binder composition, the polyfunctional amine employed, and the mechanical properties of the cured propellants are set forth in Table 11. In each example a control propellant was prepared without the addition of polyfunctional amine and was tested for mechanical properties for comparison purposes.

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" TABLE 111 w ht Ex. 7 Ex. 8 Ex. Ex. 10 Ex. 11 Ex. 12

erg Propellant composition component percent TE'IAL? Control TEIAL2 TE'IAI'2 Control 'IEIAI'2 'IETAI-2 Control 'IETAI-2 Amine additive 5 0. 0135 0 0. 030 0. 0135 0 0. 030 0. 0135 0 0. 030

Ammonium perchlorate:

Ratio, epoxide/carboxyl (equivalents) Ratio, diepoxide/tn'epoxide (equivalents) 6.5/1 6.5/1 6. 5/1 6. 5/1 6.5/1 6. 5/1 6. 5/1

Mechanical properties 3 (maximum stress) at 170 F.:

Modulus (p.s.i.) 388 348 308 452 533 428 298 398 419 Tensile strength p.s.i.) 65 44 56 67 51 04 43 23 37 Elongation (percent) 40 23 39 34 16 34 53 46 58 Mechanical IIOJeItleS 4 (maximum stress) at 77 F.:

Modulus (p.s.i.) 710 680 450 606 908 620 499 745 568 Tensile strength (p.s.i.) 97 86 82 101 84 93 87 85 86 Elongation (percent) 48 43 47 52 31 43 51 42 Mechanical properties 5 (maximum stress) at F.:

Modulus (p.s.i.) 6, 300 5, 520 5, 780 5, 190 8, 330 6, 643 5, 853 6, 643 6, 680 Tensile strength (p. 387 316 407 349 413 409 437 409 432 Elongation (percent). 48 25 41 10 22 31 22 2G Creep life at 77 F. and 65 p.s.

stress (hrs) 35 20 min. 3.5 48 20 min. 20 24 20min. 13 Mix viscosity (centipoises X10 at 140 F. at the end of propellant mixing) 700 720 816 504 701 672 481 590 639 1 TEIA is triethylenetetramine.

2 All 'IE'IA containing propellants fail in the binder; all control propellants fail at the binder-filler interface.

3 Strain rate of 0.074 in./in./min.

4 Strain rate ol 0.74 in./1n./min. 139 5 Strain rate of 74 in./in./min.

Carboxylated rubber, 8.626; diepoxide, 0.417; triepoxide, 0.064; catalyst, 0.079; hydrocarbon plasticizer, 1.882; ester plasticizer, 1.02.

propellant in the binder phase, i.e., dewetting is sub- Examples 7, 8, 9, l0, ll,and 12 (Table III) illustrate stantially eliminated. Microstructure failure analysis of both improved tensile strengths and elongations from the control propellant at the same test conditions propellant prepared with triethylenetetramine as the showed failure at the binder-filler interface illustrating polyfunctional amine and, in addition, the effect of dewetting. concentration of triethylenetetramine on mechanical Examples 2 and 3 illustrate improved tensile 4 properties and mix viscosity. At 0.0135 percent constrengths, elongations, and improved creep properties nt a (Ex mpl and 1 the tensile r g compared to the control rounds. Propellants of Examand elongation of the propellant is significantly better ples 2 and 3 employ triethylenetetramine as the polythan at the 0.030 percent concentration level (Examfunctional amine and fail in the binder phase when subples 8, l0, and 12) and resistance to creep failure is imjected to high stress. The control propellants dewet i.e., 45 proved markedly. Also at the 0.0135 percent concenfail at the binder-filler interface as determined by mitration level the mix viscosity is reduced significantly crostructure analysis when subjected to the same test. (Examples 9 and l 1). At the 0.030 percent concentra- Examples 4 and 5 illustrate improved elongation and tion level the mix viscosity is increased about 13 pertensile strengths of propellant compositions of this incent (Example 8) and about 8 percent (Example 12). vention over the control propellants when employing The addition of 0.0135 percent triethylenetetramine in tetraethylenepentamine and polyethyleneimine as the Example 9 reduced the mix viscosity 28 percent compolyfunctional amine. The control propellants of Expared to the control sample and gave a propellant that amples 4 and 5 dewet at the binder-filler interface as appeared to have infinite creep life at 65 psi. determined by microstructure analysis when subjected to the same testing conditions.

Example 6 illustrates the importance of concentra- E l 13-18 tion of the polyfunctional amine in achieving improvement in mechanical properties. ,When the percentage 7 of triethylenetetramine is increased to 0.06 percent by Six additional propellant compositions are prepared weight, inferior mechanical properties result. employing fl-(4- i h 1) thylamine (APE) a the polyfunctional amine following the general mixing procedure set forth for Examples 16. Propellant composi- Six additional propellant compositions are prepared tions and results of testing are set forth in Table IV.

Examples 71 2 Ex. 15 Ex. 16 Ex. 18 Ex. 17 APE L2 Control APE L2 Control APE APE Control TABLE IV Ex. 14 Control APE L? Weight percent Propellant composition component Example 13 illustrates that at the 0.002 percent concentration level, APE has very little effect on mechanical properties or microstructural failure mode. This propellant and its control both fail at the binder-filler 5 interface. However, at this low amine level the mix viscosity is reduced about 18 percent.

Examples 14 through 18 illustrate that at APE levels between 0.0113 and 0.060 percent, failure occurs exclusively in the binder phase whereas the corresponding control propellants fail at the binder-filler interface (dewetting). At these levels, resistance to creep failure is markedly improved.

Examples 14 and I5 illustrate that the upper limit of usefulness of APE appears to be about 0.060 percent 15 in a diepoxide crosslinked carboxy-terminated rubber binder. At this concentration level (Example 15) the creep life is extended from minutes (control) to 5.5 hours. At the 0.040 percent concentration level of Example 14, the propellant appears to have infinite creep 20 life as evidenced by the fact that after 48 hours the rate of change of elongation with time is zero. The improvement in tensile strength and elongation is considerably greater at the lower (0.040 percent) APE concentration level. The mix viscosity is decreased significantly atboth levels.

Example 16' illustrates that infinite creep life is obtained at APE concentration levels as low as 0.0113

percent.

Examples 17 and 18 illustrate that at an epoxide to carboxyl ratio of 1.08/10, somewhat better mechanical properties are obtained with APE concentration levels of 0.01 13 percent (Example 17) than at 0.020 percent (Example 18). in both cases the resulting propellants appear to have infinite creep life.

All of the control propellants for Examples 1 through 18 fail the creep test at 77F and 65 psi in less than 20 minutes. Conversely, the propellant compositions of this invention can be tailored to have a very long creep life as exemplified in Examples 9, l4, l6, l7 and 18.

The propellant compositions of this invention prepared in Examples l-l 8 showed no porosity. While ammonia gas is liberated during mixing of the compositions, the amount of ammonia gas liberated is so small due to the small quantities of polyfunctional amine employed that substantially no porosity results.

The propellant compositions of this invention have the following general compositions:

570/150 F. 430ll57 F.

1 04 1 00 0 5 1 0 5 1 367 378 526 66 5s 83 29 20 21 3 588 540 S6 98 110 31 a0 26 7, 280 7,080 8, 000 10, 100 595 056 500 31 3s 15 4s 5 .5 20 min. sea 135 F. 528/140 F. 720/140 F. e o 141 F. Lo) 0 7, 400 507 405 17 17 7 min.

21 min.

J A Jr 0 Component Weight Oxygen Containing Ammonium Salt -90 Cured Binder 520 Polyfunctional Organic Amine 0.0050.05 Metal Fuel 0-20 I I I l I I Preferably, the propellant composition contains by weight from about to about percent oxidizer and from about 5 to about 20 percent cured binder. The cured binder includes the binder prepolymer and crosslinking agent. A curing catalyst is employed as needed. From about 40 to about weight percent of the cured binder in the formulation is binder prepolymer, from about 1 to about 10 weightpercent is the crosslinking agent, and the binder plasticizer can be from about 0 to about 50 weight percent, and preferably is from about 20 to about 40 weight percent of the binder.

The composite propellant of this invention can also contain other additives such as metal fuels, plasticizers, and the various compounding ingredients commonly employed in making composite propellants, as for exes 4 (m'aximuni'rii'iiiii ii Ex. 14-18 fail in the binder phase; the APE containing propellant of Ex. 13 and all control propellants fail at the binder-filler interface. or

LII

Elongation (percent) Creep life at 77 F. and 65 p.s.i. (initial stress) (hrs.)

1 APE is fi-(4-aminophenyl)cthylamin0.

2 The APE containing propellants in 3 Strain Rate 01' 0.074 in./in./min.

4 Strain Rate of 0.74 in./in./min.

5 Strain Rate of 74 in./in./min.

'Carboxyloted rubber, 7.727; diepoxide, 0.301; Triepoxide, 0.060; catalyst, 0.0108; hydrocarbon plasticizer, 1.906; ester plasticizer, 1.00. O\

Mix viscosity (centipoisesXlO at F. at the 0nd of propellant 1nixing) ample, oxidation inhibitors, reinforcing agents, wetting agents, surfactants, ballistic modifiers, radar attenuators, and the like. In this connection, metal fuels such as powdered aluminum, beryllium, magnesium, zirconium or boron, alloys such as the aluminum alloys of boron, magnesium, manganese, copper, and the like, and plasticizers such as dioctyl phthalate, dicotyl azelate, dioctyl adipate, dodecyl adipate, polybutadiene, polyisobutylene, and the like can be utilized. Surfactants such as lecithin or mixtures of sorbitan monooleate and polyoxyethylene esters of mixed fatty and resin acids; ballistic modifiers such as di-n-butyl ferrocene, iron oxide, chromium oxide or oxamide, and radar attenuators such as molybdenum trioxide, can also be present in minor amounts in the propellant composition of this invention.

What I claim and desire to protect by Letters Patent l. A composite propellant composition comprising in the form of a cured admixture:

a. an oxidizer consisting essentially of an oxygen containing ammonium salt selected from the group consisting of ammonium perchlorate, ammonium nitrate, hydrazine perchlorate, hydrazine diperchlorate, and mixtures thereof,

b. a crosslinkable binder prepolymer having reactive functional groups selected from the group consisting of hydroxyl, carboxyl and isocyanate groups and a crosslinking agent therefore said crosslinking agent having reactive functional groups selected from the groups consisting of polyepoxides, polyisocyanates, polythioisocyanates, and polyimines,

c. a polyfunctional amine selected from the polyethyleneimine and amines having the general formula l l. HZN x NHR where X is either a) (CH ),,,Ar or said propellant composition comprising by weight from about 60 to about percent of said oxygen containing ammonium salts, from about 5 to about 20 percent of crosslinkable binder prepolymer and crosslinking agent and from about 0.005 to about 0.05 percent of polyfunctional amine.

2. The composite propellant composition of claim 1 in which the polyfunctional amine is of the general formula (I) wherein X is (NHRI): l l

wherein z is O, l, 2, 3 or 4, and R is hydrogen or lower alkyl having from one to four carbon atoms and R is hydrogen.

3. The propellant composition of claim 1 wherein the polyfunctional amine is triethylenetetramine.

4. The propellant composition of claim 1 wherein the polyfunctional amine is tetraethylenepentamine.

5. The propellant composition of claim 1 wherein the polyfunctional amine is diethylenetriamine.

6. The propellant composition of claim 1 wherein the polyfunctional amine is polyethyleneimine.

7. The propellant composition of claim 1 wherein the polyfunctional amine is B-(4-aminophenyl) ethylam- 8. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a carboxyl terminated prepolymer, and the crosslinking agent is a mixture of diepoxides and trie poxides.

9. The composite propellant composition of claim 8 wherein the polyfunctional amine is B-(4- aminophenyl) ethylamine.

10. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a hydroxyl terminated prepolymer, and the crosslinking agent is a polyisocyanate.

11. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a carboxyl terminated prepolymer, and the crosslinking agent is a polyimine.

Po-ww v UNITED STATES PATENT OFFICE (5/69) CERTIFICATE @F 'CURRECTIGN V Patent No. 3l79ol4l6 Dated February 5; 1974 Inventofla) Henry C- Dehm It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F a W Column 9 & l0 Table II;

Under Example 5, left hand column labled PEI the Modulas (p.s.i.) determined at 170 F should read 419, not 41.9 and,

The Elongation (percent) determined at 77F should read 36, not 96.

Signed and v sealed this 16th day of July 1974 I L) a .1 a j 2 Attest:

MCCOY M. GIBSON, JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents Po-ww v UNITED STATES PATENT OFFICE CERTIFICAT F CQECTIN Patent No 317901416 Dated February 5, Inventor) Henry C. Dehm It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

F a W Column 9 & l0 Table II;

Under Example 5, left hand column labled PEI the Modulas (p.s.i.) determined at 170 F should read 419, not 41.9 and,

The Elongation (percent) determined at 77F should read 36, not 96.

Signed and v sealed this 16th day of July 1974 I L) a .1 a j 2 Attest:

MCCOY M. GIBSON, JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents mg a UNITED STATES PATENT OFFICE t CERTIFICATE OF CORRECTION Patent No. 416 Dated r ary 5, 1974 Henr C. Dehm Inventor-(s) y It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 9 & l0 Table II;

Under Example 5, left hand column labled PEI the Modulas (p.s.i.) determined at 170 F should read 419, not 41.9 and,

The Elongation (percent) determined at 77F should read 36, not 96. I

Signed andhsealed this 16th day of July l974.'

- 1 I I j a a Attest: 1 1

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer I V i Commissioner of Patents 

2. The composite propellant composition of claim 1 in which the polyfunctional amine is of the general formula (I) wherein X is
 3. The propellant composition of claim 1 wherein the polyfunctional amine is triethylenetetramine.
 4. The propellant composition of claim 1 wherein the polyfunctional amine is tetraethylenepentamine.
 5. The propellant composition of claim 1 wherein the polyfunctional amine is diethylenetriamine.
 6. The propellant composition of claim 1 wherein the polyfunctional amine is polyethyleneimine.
 7. The propellant composition of claim 1 wherein the polyfunctional amine is Beta -(4-aminophenyl) ethylamine.
 8. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a carboxyl terminated prepolymer, and the crosslinking agent is a mixture of diepoxides and triepoxides.
 9. The composite propellant composition of claim 8 wherein the polyfunctional amine is Beta -(4-aminophenyl) ethylamine.
 10. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a hydroxyl terminated prepolymer, and the crosslinking agent is a polyisocyanate.
 11. The composite propellant composition of claim 1 wherein the oxygen containing ammonium salt is ammonium perchlorate, the crosslinkable binder prepolymer is a carboxyl terminated prepolymer, and the crosslinking agent is a polyimine. 